1. Field of the Invention
The invention relates to display systems and in the preferred embodiment to a display system for displaying ground maps produced by utilizing doppler radar video signals.
2. Description of the Prior Art
The azimuth resolution of real beam radar systems is determined by the antenna beamwidth. To overcome this limitation the frequency shift (doppler effect) that occurs between the transmitter and the target due to their relative velocity is used to sort out targets inside the beam. Every point on the ground can be defined by an airborne ground map doppler radar system by its range and doppler frequency. Range is necessary because a given doppler frequency defines a locus of points that make up a hyperbola that is called "isodop" or a line of constant doppler frequency. The range dimension then defines a point along any isodop. Therefore, doppler radar systems that process all ranges of interest from the return for any given output pulse at a given doppler frequency can only map along a single isodop. To scan an area on the ground requires processing a number of returns at different doppler frequencies.
The usual ground map display system works on true azimuth and range outputs from a radar. If this approach is used to display video from the doppler radar system, severe distortion of the map occurs. The system which is the subject of this invention, overcomes this display problem by generating a non-linear raster which has the same basic geometrical form as the isodops.